This invention relates to a method and apparatus for adjusting die clearance for an extruder producing a sheet, film or coating on a magnetic record of a thermoplastic resin, cellulose, rubber and the like, paper, cellophane hopper or printing ink and the like.
In a die device for molding a sheet or film of this kind (hereinafter referred to as the "sheet"), as shown in FIGS. 1 and 2, the size of die clearance 11 is adjusted by pushing or pulling a plurality of bolts 12 disposed in the direction of width in order to change the pushing force acting upon a backface 15 of an upper die element 13 and to thereby adjust the degree of bending at a neck portion 14 of upper die element 13.
However, upper die element 13 is a continuous body and when a specified bolt is manipulated, the die clearance changes not only at the position where that specified bolt acts but also at the other portions. This phenomenon is referred to as the "mutual interference effect". Ideally, the effects should be additive according to the "principle of superposition". Unfortunately, they are not. Thus, as shown in FIG. 3, the lip deviation when only the eighth bolt of twenty-two adjusting bolts is manipulated (curve a) or when only the fifteenth (curve b) is manipulated cannot be added to determine the deviation when both eighth and fifteenth (curve c) are manipulated. Thus, at the position of the 8th bolt curve a is 30, curve b is 10 and curve c is 35, not 40.
The adjustment of die clearance has been mostly carried out empirically through manual work of an operator. Therefore, some difference for adjusting occurs from operator to operator, resulting in low accuracy of die clearance, time-consuming adjustment and danger in adjustment.